Considerable work has been done in the prior art in providing automatic machines. In some cases it is desirable to provide a machine with instructions concerning operations of the machine on a workpiece, and numerically controlled machines are well known for effecting this. In other situations, it is desirable for there to be provided automatic guidance means for guiding workpieces through a machine or for guiding a machine over a surface, such as a floor. Numerous attempts have been made in the prior art to provide such automatic guidance systems. For example, U.K. Patent Specification No. 1,063,001 describes a sewing machine in which a cam controlled linkage is used to guide the workpiece along a desired path through the machine. This arrangement requires a special cam to be constructed every time the path of the workpiece is required to be changed. Thus this system is rather impractical and lacks versatility.
It has also been proposed to guide workpieces through a machine by sensing the edge thereof, so that operations can be carried out on the workpiece along a line parallel to the edge. Mechanical sensors have been proposed for feeling the edge, and photoelectric detectors have also been proposed for sensing the edge. Examples of such systems can be found in U.K. Patent Specification Nos. 1,205,290; 962,160; 1,002,283; 1,002,281; and 989,874; and U.S. Patent No. 3,925,713 also relates to such a system. Also reference may be made for further examples of such systems to the "Journal of the Apparel Research Foundation", 1970, Vol. 4, No. 2, Pages 1 to 4 and issue No. 4 of the same volume, at pages 17 to 22. These articles have been abstracted in "World Textile Abstracts" 1971/247 and 1972/916. At the time of execution of this application, the inventors have access only to the abstracts but it appears from consideration thereof that the systems described involve a photoelectric line follower which responds to a line drawing, which drawing has to be replaced in the machine each time the path to be followed is to be changed.
Thus, the edge following systems are generally insufficiently versatile for widespread application, and the photoelectric line following system is prone to errors since the operator of the machine has to ensure that the line drawing provided to the machine is the correct one for the particular workpiece to be operated upon.
There therefore exists a need for an improved control system for machines, especially in industries where the finished product is an assembly of two or more parts of variable and irregular shape. This is exemplified by the footwear and garment industries in which irregularly shaped components are cut from a variety of materials, generally in flexible sheet form, and are converted into useful products by a number of assembly and other operations. Much of the assembly depends upon the combining of components at a common line or point by such means as sewing, stapling, welding or sticking with adhesive. At present the components are generally located and guided through the combining machine manually. Thus in the closing of shoe uppers by sewing together cut components the latter are guided by hand through a sewing machine and seamed at a premarked line. This operation has a high labour content and cost, and requires skill and dexterity on the part of the operative. The need to cater for both a wide variety of styles and many sizes within each style leads to relatively small production runs of each individual item. This renders many well known automatic systems, or aids to semi-automatic production such as those based on jigs or templates, unattractive for practical and economic reasons.
It has also been considered, though possibly not published, that lines of magnetic ink could be provided on workpieces for magnetic detection by a guidance system provided in a machine through which the workpiece is to be automatically guided. This proposal, however, would generally involve a visible line on the workpiece, which would be unacceptable in many industries, especially the shoe industry.